Disc winding with integral load current carrying rib shielding

ABSTRACT

In electrical transformers of the type which utilize a plurality of axially spaced disc coils connected to form a winding, a turn arrangement for more uniformly distributing surge potentials across and within the winding wherein certain current carrying turns are utilized to provide additional transient current paths through the winding upon the occurrence of a voltage surge.

United States Patent [191 Gearhart 111 r 3,715,696 [451 Feb. 6, 1973 [75] Inventor:

541 DISC WINDING WITH INTEGRAL LOAD CURRENT CARRYING RIB- SHIELDING 4.

[52] US. Cl ..1.....336/70 3,63 I367 l2/l97i Dutton et ai. ..336/70 FOREIGN PATENTS OR APPLICATIONS 862,267 3/1961 Great Britain ..336/l87 I 271,499 6/1965 Australia ..336/187 Primary ExaminerThomas J. Kozma AttorneyFrancis X. Doyle [57] l I ABSTRACT In electrical transformers of the type which utilize a 5 1] Inner. .1101: 15/14 plurality Of axially Waced disccoils connected to form [58] Field or Search. ..336/69 70 I86 187 a n arrangement 7 p f tributing surg'e potentials across and within the winding wherein certain current carrying turns are utilized {56] References Cited. to provide additional transient current paths through I UNITED STATES PATENTS I the winding upon the occurrence of a voltage surge.

3,479,629 11/1969 Broszat ..'....'.....336/70 6 Claims, 4 Drawing Figures 7 m au/v5 I a zooA i/ 2005 ZOIA WI ++++-+1- 81 l e- DISC WINDING WITII INTEGRAL LOAD CURRENT CARRYING RIB SIIIELDING BACKGROUND ANDOBJECTS OF THE I INVENTION My invention relates in general to electrical inductive apparatus, such as transformers and more particularly to a means for improving the voltage distribution through a winding and reducing insulation stresses oc curring therein upon the application of steep wave impulse voltages such as lighting or switching surges. The following published art, now known to applicant, is exemplary of prior art approaches relevant in this area of technology: U.S. Pat. No. 1,585,448-Weed; U.S. Pat. No. 3,l60,838Bedil: U.S. Pat. No. 3,221,282-Brierley et al.; U.S. Pat. No. 3,380,007-Alverson et 'al.; and U.S. Pat. No. 3,'479,629-Brozat.

It is well known that highly inductive windings such as iron core transformer and reactor windings, when exposed to steep wave front impulse or transient voltages, exhibit initially an exponential distribution of voltage drop along the length of the windings with a very high voltage gradient at the first few turns. For example, approximately 60 percent of the voltage may appear across the first 5 percent of the turns of the winding at the high voltage end. This extremely nonuniform voltage distribution is due primarily to the unavoidable distributed capacitance between each incremental part of the winding and adjacent grounded parts such as the coreand casing structure. Such ground capacitance is referred toas ,parallel" capacitance when the low voltage .terminal of the winding is grounded in the usual manner. Such a winding inherently possesses also a distributive capacitance between turns, the sum of such capacitance being in series between theywinding terminals. If this series capacitance alone were present, voltage distribution throughout the winding would be substantially uniform and linear, as it would be also if inductance alone were' present. However, since distributive capacitance both series and parallel, is an inherent winding characteristic, voltage distribution in the presence of impulse voltages, suchas lightning or switching surges, is a design consideration of importance.

One common type of high voltage winding for transformers and reactors is a continuous disc winding. In such a winding each of a plurality'of annular (disc) coils is wound as a radial spiral, the coils beingdisposed coaxially on a core and connected electrically in a sequential series circuit relation with adjacent coils being wound in alternate rotational directions. As is known, continuous disc windings are characterized'by relatively low seriescapacitance and as a consequence such windings have relatively poor surge voltagedistribution characteristic.

Since the initial'voltage distribution in a transformer winding subjected. to a steep-fronted voltage wave at the terminal thereof is a function of the ratio of the parallel capacitance (i.e., capacitance to ground) to the series capacitance of the winding, continuous disc windings are subject to insulation'failureresulting from a poor initial voltage distribution in the event of a voltage surge.

The most practical way to improve the voltage distribution of a disc winding is to increase its series capacitance and many techniques are known for increasing such capacitance. One such technique is to provide electrical conductors surrounding the outside turns of various coils in the winding. These conductors are commonly referred to as rib shields. The rib shields surrounding the coils of the winding closest the line end are normally electrically connected to the line terminal whereas rib shields surrounding interior coils may be electrically connected to interior turns of the windings.

As is known the use of rib shields increase the through-series-capacitance of the winding and offer the transient current which results from a voltage surge and which would normally flow to ground via the disc coils an alternate path through the winding via a series path of the rib shields and their adjacent disc coils. By keeping the transient current flowing through the winding (as opposed to letting it flow directly to ground via the separate disc-coils) a more linear voltage distribution across the winding results.

The improved surge voltage distribution characteristic attained by a use of rib shields" is not without its price since the use of such shields results in relatively large windings due to the fact that (l) rib shields are not available for carrying load current and thus are winding extras" in terms of normal operation and (2) rib shields must be heavily insulated to prevent arcing between them and mechanically adjacent coil portions. Furthermore, the use of rib shields necessitates numerous joints (e.g., brazed connections) to connect the shields to the winding. This results in increasing winding costs.

It is a general object of my invention to provide a new and improved winding structure for electrical inductive apparatus which aids in distributing surge potentials more uniformly across the electrical winding.

It is yet a further object of my invention to provide a new and improved winding structure for electrical inductive apparatus which has an improved surge potential distribution characteristic and which may be constructed with very little or no increase in cost and which does not substantially change conventional winding techniques.

SUMMARY OF THE INVENTION In accordance with one aspect of my invention 1 provide a disc-type winding in which certain load current carrying turns are utilized to provide additional transient current paths through the winding like those resulting from the use of conventional rib shields. The additional current paths result in a more uniform surge voltage distribution throughout the winding. By utilizing load current conducting turns themselves like rib shields, smaller and cheaper comparable rating windings can be manufactured than can be manufactured utilizing conventional rib shields.

BRIEF DESCRIPTION OF THE DRAWINGS My invention will be better understood and its various objects and advantages will be more fully appreciated from the following description in conjunction with the accompanying drawings in which:

FIG. I' is a schematic diagram of a portion of an electric transformer having a high voltage disc-type winding in accordance with one embodiment of my invention;

FIG. 2 is a schematic diagram of a portion of an electric transformer having a high voltage disc-type winding in accordance with another embodiment of my invention;

FIG. 3 is a schematic diagram of a portion of an electric transformer having a high voltage disc-type winding in accordance with yet another embodiment of my invention;

FIG. 4 is a schematic diagram of a portion of an electric transformer having a high voltage disc-type winding in accordance with yet another embodiment of my invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings, I have shown in cross section in FIG. 1 a core type electric induction apparatus having a magnetic core 101 including plural parallel legs (only one of which is shown) upon each of which are mounted current conducting windings indicated generally by reference numeral 102. Each winding 102 in the case of a typical core type transformer, comprises a low voltage primary winding 110 of tubular configuration closely surrounding the core 101 and a high voltage secondary winding 11 of the disc-type concentrically surrounding the low voltage winding. The low voltage winding 110 is encased in a suitable insulating sheath 112. The space between the low voltage winding and the core 101 is filled at least partially by a tubular insulating spacer 113. The radial space between the low voltage winding 110 and the high voltage winding 111 is referred to as the transformer main gap, and a tubular insulating sleeve 114 is provided in this space.

It will be understood as the description proceeds that while I have shown for the purpose of illustration a core type transformer having a primary winding section and a secondary winding section on a core leg, my invention is equally applicable to other type of transformers and to reactors or other apparatus including high voltage inductive windings whether of the single phase or multi phase type. My invention itself concerns more particularly the structure and configuration of the high voltage winding. In the case illustrated the invention concerns the high voltage primary winding 111 of'the transformer. Reference will be had hereinafter, therefore, more particularly to the fragmentary cross-sectional view of FIG. 1 in which one half of the high voltage winding 111 is shown. It will be understood that although the half of thehigh voltage winding shown includes 12 connected annular coils, the winding may be made up of any number of coils as may be desired in accordance with the voltage rating thereof.

As can be seen winding 111 includes a plurality of annular sections or coils 200 through 211, inclusive, each of which is wound of a spiral conductor. As illustrated, the spiral conductor forming the coils of windnumeral 212 and includes coils 200 through 205, inclusive, each of which are wound in accordance with my invention. The mid-portion of the winding 111 is denoted by the numeral 213 and includes coils 206 through 211, inclusive, each of which are wound and connected in the conventional continuous disc winding manner.

Each coil in the end portion 212 of winding 111 includes a major and a minor portion. The major portion of each coil is denoted by the letter A and forms an interior part of the winding (i.e., is adjacent to the low voltage winding and the minor portion of each coil is denoted by the letter B and forms an exterior part of the winding. The major portion of each coil is formed of a plurality of turns connected in a sequential series circuit. For example, major portion 200A of coil 200 is formed of the sequential series connection of conductor turns 1 through 9. Turn 1 is connected to a line terminal of the winding 111 and forms a first end of the major portion 200A. Turn 9 forms the second end of that major portion. Major portions 201A through 205A are wound in a similar manner and turn 18 forms the first end of major portion 201A and turn 10 forms the second end thereof, turn 22 forms the first end of major portion 202A and turn 30 forms the second end thereof, turn 39 forms the first end of major portion 203A and turn 31 forms the second end thereof, turn 44 forms the first end of the major portion 204A and turn 52 forms the second end thereof and turn 61 forms the first end of major portion 205A and turn 53 forms the second end thereof.

The minor portions of each coil is composed of N turns (N being an integer) wound in one rotational direction. In the embodiment shown in FIG. 1 the integer N equals 27 i.e., the minor portion of each coil is composed of 2 turns. For example, the minor portion 2008 of coil 200 is composed of turns 19 and 20, turn 19 being the first turn of the minor portion and turn 20 being the Nth (second) turn thereof. In a similar manner turn 21 is the first turn of minor portion 2018 and turn 41 is the Nth turn thereof, turn 40 is the first turn of the minor portion 2028 and turn 42 is the Nth turn thereof, turn 43 is the first turn of the minor portion 203B'and turn 63 is the Nth turn thereof, turn 62 is the first turn of the minor portion 20413 and turn 64 is the Nth turn thereof and turn 65 is the first turn of the minor portion 2058 and turn 66 is the Nth turn thereof.

The first end turn of the major portion of each coil is disposed immediately adjacent to the first turn of the minor portion thereof.

The second end turn of the major portion of a coil and the Nth turn of the minor portion of the coil form first and second ends of the coil, respectively.

The coils of portion 212 are disposed coaxially on the core with the major portions of adjacent coils being wound in alternate rotational directions. The coils of portion 213 are also disposed coaxially on the core and adjacent coils thereof are wound in alternate rotational directions. The spacing between adjacent coils forms a duct in which a cooling medium, e.g., oil, may be disposed.

' In accordance with my invention I utilize the minor portions of the coils to increase the through-seriescapacitance of the winding in a manner similar to that accomplished via the use of conventional rib shields. However since the minor portions of the winding are load current carrying members, the improved surge voltage distribution capability of my winding is not achieved at the expense of winding size and cost as is the case with the use of conventional rib shields. To that end the first end turn of the major portion of each coil in the end portion 212 of the winding is serially connected to the the first turn of the minor portion of the immediately preceding coil in that portion of the winding and the Nth turn of the minor portion of each coil is directly connected to the penultimate turn of the minor portion of the immediatelysucceeding coil of said end portion.

In the embodiment shown in FIG; 1 the first'end turn of the major portion 201A, i.e., turn 18, is directly connected to the first turn, i.e.,turn19, of the minor portion 20013 of the immediately preceding, and in this case, end coil 200. The Nth turn of the minor portion 2003 of coil 200,i.e., turn 20, is directly connected to the penultimate turn,-and in this case first turn, i.e., turn 21, of the minor portion of coil 201.

In a similar manner the first end turn of the major portion 202B, i.e., turn 22, is connected to the first turn, i.e., turn 21, of the minor portion of the immediately preceding coil 201. The Nth turn of the minor portion of coil 201, i.e., turn 41 is directly connected to the penultimate turn, i.e., turn 40, of the minor portion of the immediately succeeding coil 202.

The turns 1 through 132 as shown in FIG. l are electrically connected in a sequential'series circuit in numerical order. To that end, in winding portion 212 there is a direct connection between the first. end of coils 200 and 201 (via the connection between turns 9 and 10), a direct connection between the first end of coils 202 and 203 (via the connection between turns 30 and 31), and a directconnection between the first end of coils 204 and 205 (via the connection between turns 52 and 53). The Nth turn of coil- 205 is, i.e., turn 66, directly connected to the first turn, i.e., turn 67 of the continuous disc portion 213 ofwinding 111.

The operation ofthe minor portions of coils 200 through 205 in distributing voltage across the winding.

in the event of a voltage surge appearing'at the line terminal is as follows. Turn 19 of minor portion 2003 is capacitively coupled to turn 1 of major portion 200A.

Upon the incidence of a voltage surge at the line, terminal, turn 1 tends to raise the potential on turn 19 to a level approaching that on turn 1. Turn 18v is directly connected to turn 19 and is capacitively coupled thereto via turns 21 and 20. Accordingly,' the potential on turn 18'resulting from the surge tends to approach the potential on the line terminal. Turn 22 is directly connected to turn 21 and is capacitively coupled I thereto via turns 41 and40. Accordingly, the potential portions. For' example, the capacitance between turns 1 i parallel capacitances add like series resistances, the series capacitance through coils 200 and 201 is increased.

As can be seen in the embodiment of FIG. 1 the inner portion of winding 111 is wound in the conventional continuous disc manner in the interest of winding economy. Although the continuous disc portion of the winding will exhibit a lower through series capacitance than winding portion 212, such a construction is acceptable particularly for use in applications wherein cost reduction is a primary criteria. It should be pointed out at this point that the entire winding can if desired be-wound in the manner of winding portion 212 with no continuous disc coils. For many applications such a construction is preferable.

FIG. 2 is a schematic diagram of another embodiment of my invention. As can be seen the high voltage winding 111 includes 12 annular coils 200 through 21 1, none of which are continuous disc coils. The minor portions of these coils are also denoted by the letter B andinclude N=3 turns.

It should be noted that in accordance with my invention the minor portions of each coil may have as many or as few turns as desired (i.e., N can be any integer).

In the winding shown in FIG. 2 the first end turn of the major portion of each coil is serially connected to the first turn of the minor portion of the immediately preceding coil, the first turn of the minor portion of each coil is serially connected to the second turn of the minor portion of the immediately preceding coil and the Nth turn of the minor portion of each coil is serially connected to the penultimate turn of the minor portion of the immediately succeeding coil. For example, first end turn 16 of coil 201 is serially connected to the first turn, i.e., turn 17, of the minor portion 200B of the immediately preceding coil 200, the first turn, '19, of the minor portion 2018 is serially connected to the second turn, i.e., turn 18, of the minor portion 2008 of the immediately preceding coil 200 and the Nth turn, i.e., turn 38, of the minor portion 2008 of coil 200 is serially connected to the penultimate turn, i.e., turn 37, of the minor portion 201B of the immediately succeeding coil 201. I

FIG. 3 is a schematic diagram of yet another embodiment of my invention. This embodiment, like that voltage and that the higher the numbered turns the smaller the voltage appearing thereon.

The above described action of the minor portions of my inventive winding in improving the voltage distribution throughout is attributable to increased series capacitance through the winding produced -by such shown in FIG. 1, includes a continuous disk winding portion 213, however, the minor portion of each coil in the end portion 212 of the winding contains only a single turn, i.e., N =1. The embodiment shown in FIG. 3 exhibits a lower through-series-capacitance than the embodiment shown in FIGS. 1 or 2.

' FIG. 4 is a schematic diagram of yet another embodiment of my invention wherein the minor portion of each c'oil includes N=2 turns. The winding has associated therewith static plates 220 (only one of which is shown) of conventional construction. As can be seen the static plate 220 is connected to the line terminal.

Theme of the static plate increases the capacitive coupling between turns 1 and 19 over the existing between turns 1 and 19 in FIG. 1 due to the factthat in FIG. 4 turn 19 is capacitively coupled to turn 1 in two ways, i.e., one way being via the insulation separating them and the other way being via the static plate. Ac-

cordingly, the through-series capacitance of winding 111 of FIG. 4 is enchanced.

As can be seen in FIG. 4 inter-turn insulation strips 230 are placed between turns which are mechanically adjacent in the various coils but which-are electrically separated from one another by a considerable number of turns. For example, such strips are used between turns 1 and 19 of coil 200, turns 21 and 41 of coil 201, turns 22 and 40 of coil 202, turns 43 and 63 of coil 203, turns 44 and 62 of coil 204, turns 65 and 85 of coil 205, turns 66 and 84 of coil 206, turns8'l and 107 of coil 207, turns 88 and 106 of coil 208, turns 109 and 129 of coil 209, an turns 110 and 128 of coil 210. The use of the insulation strips 230 permit a lesser amount of turn insulation than would otherwise be required due -to the voltage difference between adjacent turns. v

While I have shown and described a particular em"- bodiment of my invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from my invention in its broader aspects (e.g., the minor portion of a coil may form an inner part of the winding and the major portion thereof form an exterior part of the winding and static plates can be used with all embodiments); and I, therefore, intend herein to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In an inductive disc winding; and end portion comprising:

a. plural annular coils having a first and a second end and disposed adjacent to one another, an end one of said coils being connected to a main terminal of said winding, each of said coils comprising:

i. a major portion composed of plural turns electrically connected in a sequential series circuit, said major portion including a first and a second end turn; an

ii. aminor portion composed of N turns wound in one rotational direction starting with a first turn and ending with a Nth turn, said N being an integer, said first turn being disposed immediately adjacent to said first end turn of said major portion, said second end turn of the major portion forming the first end of the coil, said Nth turn of the minor portion forming the second end of the i coil; and b. means for connecting the coils of said winding end portion together wherein:

i. the first end turn of the major portion of each coil is serially connected to the first turn of the minor portion of the immediately preceding coil of said end portion; and

. the Nth turn of the minor portion of each coil is serially connected to the penultimate turn of the minor portion of the immediately succeeding coil of said end portion.

2. The winding as specified in claim 1 wherein N is the integer 2.

3. The winding as specified in claim 2 wherein the first end of said end coil-is serially connected to the first end of the immediately succeeding coil.

4. The winding as specified in claim 1 wherein N IS the integer 3 and wherein the first turn of the minor portion of each coil is serially connected to the second turn of the minor portion of the immediately preceding coil of said end portion.

5. The winding as specified in claim 4 wherein the first end of said coil is serially connected to the first end of the immediately succeeding coil.

6. In an inductive disc winding, an end portion comprising:

a. at least two annular coils having a first and a second end and disposed adjacent to one another, an end one of said coils being connected to a main terminal of said winding, each of said coils comprising:

i. a major portion composed of plural turns electricall'y connected in a sequential series circuit, said major portion including a first and a second end turn; and

. a minor portion composed of a single turn being disposed immediately adjacent to said first end turn of said major portion, said second end turn of the major portion forming the first end of the coil, said single turn of the minor portion forming the second end of the coil; and

. means for connecting the coils of said winding end portion together wherein:

i. the minor portion of the end coil being serially connected between the first end turn of the major portion of the immediately succeeding coil and the second end of said immediately succeeding coil. 

1. In an inductive disc winding; and end portion comprising: a. plural annular coils having a first and a second end and disposed adjacent to one another, an end one of said coils being connected to a main terminal of said winding, each of said coils comprising: i. a major portion composed of plural turns electrically connected in a sequential series circuit, said major portion including a first and a second end turn; an ii. a minor portion composed of N turns wound in one rotational direction starting with a first turn and ending with a Nth turn, said N being an integer, said first turn being disposed immediately adjacent to said first end turn of said major portion, said second end turn of the major portion forming the first end of the coil, said Nth turn of the minor portion forming the second end of the coil; and b. means for connecting the coils of said winding end portion together wherein: i. the first end turn of the major portion of each coil is serially connected to the first turn of the minor portion of the immediately preceding coil of said end portion; and ii. the Nth turn of the minor portion of each coil is serially connected to the penultimate turn of the minor portion of the immediately succeeding coil of said end portion.
 1. In an inductive disc winding; and end portion comprising: a. plural annular coils having a first and a second end and disposed adjacent to one another, an end one of said coils being connected to a main terminal of said winding, each of said coils comprising: i. a major portion composed of plural turns electrically connected in a sequential series circuit, said major portion including a first and a second end turn; an ii. a minor portion composed of N turns wound in one rotational direction starting with a first turn and ending with a Nth turn, said N being an integer, said first turn being disposed immediately adjacent to said first end turn of said major portion, said second end turn of the major portion forming the first end of the coil, said Nth turn of the minor portion forming the second end of the coil; and b. means for connecting the coils of said winding end portion together wherein: i. the first end turn of the major portion of each coil is serially connected to the first turn of the minor portion of the immediately preceding coil of said end portion; and ii. the Nth turn of the minor portion of each coil is serially connected to the penultimate turn of the minor portion of the immediately succeeding coil of said end portion.
 2. The winding as specified in claim 1 wherein N is the integer
 2. 3. The winding as specified in claim 2 wherein the first end of said end coil is serially connected to the first end of the immEdiately succeeding coil.
 4. The winding as specified in claim 1 wherein N is the integer 3 and wherein the first turn of the minor portion of each coil is serially connected to the second turn of the minor portion of the immediately preceding coil of said end portion.
 5. The winding as specified in claim 4 wherein the first end of said coil is serially connected to the first end of the immediately succeeding coil. 